Considerable interest has been generated in the field of regenerative medicine by recent work relating to the isolation and propagation of human stem cells of various kinds. Pluripotent stem cells are a particularly promising type of progenitor cell, because they can differentiate into a variety of different tissue types, and have a powerful capacity for self-renewal.
An important source of pluripotent stem cells is early embryonic tissue. Techniques have been developed recently to isolate and culture human embryonic stem (ES) cells (Thomson et al., Science 282:114, 1998; U.S. Pat. Nos. 6,090,622 & 6,200,806) and human embryonic germ (EG) cells (Shamblott et al., Proc. Natl. Acad. Sci. USA 95:13726, 1998; U.S. Pat. No. 6,090,622). International Patent Publications WO 99/20741 and WO 01/51616 (Geron Corp.) provide methods and materials for growing primate-derived primordial stem cells in feeder-free culture, which considerably facilitates the preparation of these cells and their derivatives for human therapy.
Draper et al. (J. Anat. 200:249, 2002) characterized various surface antigens on human ES cells, both before and after differentiation. They found that HLA Class I antigen, and β2 microglobulin (the light chain of Class I) were expressed in undifferentiated ES cells, and could be induced to higher levels by treatment with interferon gamma (IFN-γ). Drukker et al. (Proc. Natl. Acad. Sci. USA 99:9864, 2002) characterized the expression of MHC proteins on human embryonic stem (ES) cells. Low levels of MHC Class I antigen was found. Class I expression was higher when the cells were treated with IFN-γ, but not IFN-α OR IFN-β. After the cells were allowed to differentiate, Class I expression was enhanced after treatment by all three interferon isotypes. MHC Class II proteins and HLA-G were not expressed on undifferentiated ES cells, or after early differentiation.
Paradigms have recently been established to cause pluripotent stem cells to differentiate into relatively homogeneous populations of particular tissue types, suitable for transplantation.
U.S. Pat. No, 6,458,589 (Geron Corp.) describes and claims ES-derived cells containing a high proportion of cells having multiple characteristics of human hepatocytes. PCT publication WO 01/88104 (Geron Corp.) describes neural progenitor cell populations obtained by differentiating human ES cells. Patent Publications WO 02/42445 and GB 2374076 (Geron Corp.) provide cell populations derived from pluripotent stem cells that are purged of the undifferentiated cell phenotype.
Methods to differentiate human pluripotent stem cells into cells of the hematopoietic lineage were reported by Li et al. (Blood 15:98, 2001); U.S. Pat. No. 6,280,718 (Wisconsin); and Kaufman et al. (Proc. Natl. Acad. Sci. USA 98:10716, 2001). Coculturing with murine bone marrow cells or yolk sac endothelial cells was used to generate cells with hematopoietic markers.
US 2003/0153082 A1 (Bhatia, Robarts Institute) describes an alternative direct method for generating hematopoietic cells from human ES cells. The undifferentiated cells are put into suspension culture with a mixture of hematogenic cytokines and a bone morphogenic protein. No other cell type needs to be present. The cell populations that are produced have a high proportion of CD45+ve and CD34 +ve cells, and the capacity to generate a high frequency of primary and secondary colonies in a standard CFU assay.
Depending on tissue type, cells made by differentiating ES cells may express histocompatibility antigens capable of eliciting an allograft rejection response when administered to a human patient. Several strategies are available for preventing rejection. Traditional methods include the use of immunosuppressive drugs currently in vogue for treating recipients of solid organ transplants.
An alternative strategy is to induce tolerance in the prospective recipient, so that they accept tissue having the histocompatibility markers of the intended allograft, without otherwise being immunocompromized. Patent publication US 2002/0086005 A1 (Geron Corp.) provides a system for promoting graft acceptance, using a cell population differentiated from ES cells. The differentiated cells induce a state of specific unresponsiveness in the patient. This makes the patient able to accept another cell type made from the same ES cell line, which then regenerates a cellular function that the patient needs.
The invention described in this disclosure provides a new system for regulating the immune response in the context of regenerative medicine or treatment of autoimmune disease.